Symptoms typically begin one to five weeks after a bout of strep throat, although in some cases the infection may have been too mild to have been recognised. Sometimes, people with rheumatic fever do not recall having had a sore throat.

Rheumatic fever can also cause a temporary nervous system disorder once known as St. Vitus' dance. Today it is called chorea, or Sydenham's chorea. This is a nervous disorder -- characterised by rapid, jerky, involuntary movements of the body -- occurring mainly in childhood or during pregnancy and closely associated with rheumatic fever. It may appear up to six months after rheumatic fever has cleared. People with mild cases of chorea may find it difficult to concentrate or write. More severe cases can cause the muscles of the arms, legs or face to twitch or jerk uncontrollably.

The knees, ankles, elbows and wrists are the joints most likely to become swollen from rheumatic fever. The pain often migrates from one joint to another. However, the greatest danger from the disease is the damage it can do to the heart. In more than half of all cases, rheumatic fever scars the valves of the heart, forcing this vital organ to work harder to pump blood. Over a period of months or even years -- particularly if the disease strikes again -- this damage to the heart can lead to a serious condition known as rheumatic heart disease, which happens in up to one-third of cases and can eventually cause the heart to fail.

How common is rheumatic fever?

Before the widespread introduction of antibiotics, rheumatic fever was one of the main causes of acquired heart disease in England.

Now, thanks to antibiotics and better public sanitation and living standards, the condition is rare. It is estimated that less than one in every 100,000 people is affected by rheumatic fever in England each year.

The majority of cases of rheumatic fever affect children aged 5-15. Adults make up 20% of cases.

The condition affects both sexes equally, though girls and women tend to have more severe symptoms.

What causes rheumatic fever?

Rheumatic fever results from an inflammatory reaction to certain group A streptococcus bacteria. The body produces antibodies to fight the bacteria, but instead the antibodies attack a different target: the body's own tissues, so it is a type of autoimmune disorder. The antibodies begin with the joints and often move on to the heart and surrounding tissues. Because only a small fraction (generally fewer than 0.3%) of people with strep throat ever develop rheumatic fever, medical experts say that other factors, such as a weakened immune system, must also be involved in the development of the disease.

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